We have carried out a variety of studies on the biosynthesis, metabolism, and physiological role of putrescine and spermidine in Escherichia coli. The enzymes responsible for the biosynthesis of spermidine have been purified and characterized. The genetic location of the responsible genes have been mapped, and mutants in the respective genes have been obtained. Of particular interest are those mutants with an absolute requirement for amines for growth, and those mutants that have a temperature-dependent requirement for amines. Recombinant DNA plasmids have been constructed for each of the genes. These plasmids have been particularly useful in permitting the overproduction of the respective enzymes, and thus in providing a good source for the purification procedures. In addition, initial studies have been carried out on DNA sequencing. Particular emphasis has been placed on the plasmids containing the gene (speD) that codes for adenosylmethionine decarboxylase, since we have shown that this enzyme has an unusual prosethetic group, namely, pyruvate, which is essential for enzyme activity.